In the processing of flue gases, especially from fossil fuel power plants and the like, the flue gas may be scrubbed in a desulfurization unit having a desulfurization scrubber or absorber in which the flue gas is brought into direct contact with a scrubbing solution containing calcium carbonate (CaCO.sub.3), the scrubbing liquid collecting as a suspension in the sump of the absorber.
It is important to be able to measure the CaCO.sub.3 content of the suspension withdrawn from the sump of the absorber. Based upon this measurement, limestone metering to the scrubbing solution, namely, the addition of fresh limestone, can be controlled or determined. In the past the technique for such measurement has involved the taking of samples and subjecting the samples to a laboratory analysis for the CaCO.sub.3 content. This procedure has been expensive and, of necessity, the time between individual measurement or sampling has been excessive because each sampling was associated with an expensive analytical step.
The automated measuring system has been proposed to allow the CaCO.sub.3 content values to be obtained with shorter intervals. For example, DE-C 38 09 379 describes a continuous process in which a measurement stream is branched from the scrubbing plant or absorber, acid is added to the measurement stream to drive out CO.sub.2, partial values for CO.sub.2 like partial pressure can be measured and the CaCO.sub.3 content calculated for the branched measurement stream from the partial CO.sub.2 value. The precision and sensitivity of this process, however, leaves much to be desired.